1. Field of Invention
The present invention relates generally to safety apparatus for mobile anhydrous ammonia fertilizer systems.
More particularly the invention relates to a safety system including a safety shut-off valve provided with remote actuation to shut down the flow of anhydrous ammonia in the event of a leak in an anhydrous ammonia fertilizer system, and in the event the anhydrous ammonia nurse tank breaks-away from the tractor or implement to which it is connected.
2. Description of Prior Art
Anhydrous ammonia is a widely used source of fertilizer; it is readily available and it applies relatively easily. Anhydrous ammonia is also used to control mold growth in high moisture grains, and to add non-protein nitrogen to corn silage.
However, anhydrous ammonia is extremely dangerous. Among other things, anhydrous ammonia can cause damage to eyes, and to mucous membranes such as in the nose, mouth, and throat. Inhalation can cause damage to the lining of the lungs, inhibiting oxygen transference from the lungs into the blood stream. Exposure to high concentration levels of anhydrous ammonia can cause convulsive coughing and respiratory spasms.
Ammonia gas is colorless, but it has a sharp pungent odor that makes it easily detectable. When used as fertilizer, ammonia gas is compressed into a liquid and stored in high pressure tanks. The high pressure under which anhydrous ammonia is stored, and its caustic chemical nature, make anhydrous ammonia one of the more dangerous chemicals used in agriculture.
A typical anhydrous ammonia fertilizer system includes a high-pressure nurse tank in which the liquid anhydrous ammonia is stored and transported, a tool bar connected between the nurse tank and the back of a tractor, a set of knives extending from the tool bar into the ground to till the soil as the tool bar and nurse tank are pulled through a field by the tractor, a set of applicator tubes associated with the knives to dispense the anhydrous ammonia into the soil, a manifold to distribute the anhydrous ammonia to the applicator tubes, and a hose connected from the nurse tank to the manifold to supply anhydrous ammonia.
The anhydrous ammonia fertilizer system also typically includes an excess flow valve supplied as part of the nurse tank, a main shutoff valve connected to the nurse tank at the upstream end of the hose, a breakaway valve connected between the main shutoff valve and the downstream end of the hose, and a manifold shutoff valve connected between the manifold and the downstream end of the hose. The main shutoff valve is typically manually operated to control flow from the nurse tank to the distribution manifold, and the manifold shutoff valve is typically operated remotely via hydraulics to control the flow from the manifold to the applicator tubes.
The purpose of the breakaway valve is to automatically stop the flow of anhydrous ammonia in the event the nurse tank separates from the tractor. The breakaway shutoff valve typically consists of male and female sections that are held together such as by spring-biased ball detents. As long as the parts are together, the anhydrous ammonia will flow through unrestricted. If the hose pulls tight, the male and female parts of the breakaway valve are suppose to separate, and a spring-biased check valve located in each part is to close to shut off the flow of anhydrous ammonia, thereby preventing a rupture in the hose itself and damage to the main valve on the nurse tank.
The excess flow valve is intended to detect excess flow rates from the nurse tank, and shutdown the flow of anhydrous ammonia therefrom, such as if the hose or a hose connection ruptures, whether or not the nurse tank has separated from the toolbar. In this way, the excess flow valve also provide a backup function to a grossly malfunctioning breakaway valve.
However, even with such safety features and redundancies, anhydrous ammonia fertilizer systems still present real dangers to the operator. If a leak develops in the system, short of causing separation of the breakaway valve, or resulting in flow less than the triggering threshold of the excess flow valve, then the system operator must manually close the main shutoff valve to stop the leak. Often times, this will require the operator to be in close proximity to the escaping anhydrous ammonia, and thus, at risk of contacting and breathing the gaseous ammonia.
Hoses are typically the weakest link in an anhydrous ammonia fertilizer system. They are susceptible to soft spots, cuts, ruptures and tears; and they tend to blister, bulge, crack, and slip near couplings. If the structural integrity of a hose is compromised, anhydrous ammonia will spray out. Due to the high pressure under which the liquid ammonia is under, and expansion of the ammonia as it sprays into the atmosphere, such leaks can engulf the entire area with vaporized ammonia. As a result, the operator may need to fight his way through the cloud of vapor to reach the main shutoff valve.
And if a leak develops while fertilizing a field, the operator would need to stop the tractor, exit from the cab, and circle around the fertilizer system to reach the main shutoff valve. The time this takes results is additional hazardous ammonia being lost and sprayed into the air.
In addition, the excess flow valve and break-away valve can be unreliable and subject to malfunction. The excess flow valve is typically supplied inside the nurse tank, and is therefore not a component that the operator would normally be concerned with. And the breakaway valve is not a component that is easily checked in the field for proper or reliable operation. Therefore, these valves is often overlooked by the operator prior to undertaking fertilizer operations, and in many instances, they may be seldom actually checked for reliable or proper operation. Thus, failure of either the excess flow valve to shutdown, or failure of the check vales in the breakaway from to seal off the separated halves, can result in the above-mentioned spraying out of anhydrous ammonia into the surrounding area. In addition to the dangers associated with potential exposure to anhydrous ammonia should either of these valves malfunction, failure of the male and female halves to separate as the hose becomes too taught can also result in irreparable damage to the hose, to the main shutoff valve, and to other components connected thereto in the fertilizer system.
Consequently, there is a need for safety apparatus in an anhydrous ammonia fertilizer system that can be actuated closed at a safe distance from leaking anhydrous ammonia, that will automatically actuate closed if the hose becomes sufficiently tight to present an impending potential for a leak to develop or for damage to the hose and other components in the system, and that is further effective as a backup safety shutoff valve should either the excess flow valve or the breakaway valve fail to function properly. Thus, there is a need for a safety system including a shutoff valve that cam be actuated closed by the operator when in the tractor cab, as well as when standing or working between the cab and the nurse tank, and that is configured to automatically detect when the hose is becoming stretched to a point of danger and automatically stop the flow of anhydrous ammonia before the hose reached the point at which the breakaway valve will separate.